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1 Muscle, Ions & Exercise Group, School of Human Movement, Recreation and Performance, Victoria University of Technology, Melbourne, Victoria, Australia
2 Department of Physiology and Applied Nutrition, Australian Institute of Sport, Adelaide, South Australia, Australia
3 Department of Physiology and Applied Nutrition, Australian Institute of Sport, Canberra, Australian Capital Territory, Australia
4 School of Health Sciences, Deakin University, Melbourne, Victoria, Australia
5 Centre of Sports Studies, University of Canberra, Canberra, Australian Capital Territory, Australia
* To whom correspondence should be addressed. E-mail: michael.mckenna{at}vu.edu.au.
Athletes commonly attempt to enhance performance by training in normoxia but sleeping in hypoxia (live high and train low, LHTL). However, chronic hypoxia reduces muscle Na+,K+ATPase content, whilst fatiguing contractions reduce Na+,K+ATPase activity, which each may impair performance. We examined whether LHTL and intense exercise would decrease muscle Na+,K+ATPase activity; whether these effects would be additive and sufficient to impair performance or plasma K+ regulation. Thirteen subjects were randomly assigned to two fitness-matched groups, LHTL(n=6), or control (CON, n=7). LHTL slept at simulated moderate altitude (3000m, FIO2 15.48%) for 23 nights and lived and trained by day under normoxic conditions in Canberra (altitude ~600m); CON lived, trained and slept in normoxia. A standardized incremental exercise test was conducted before and after LHTL. A vastus lateralis muscle biopsy was taken at rest and after exercise, before and following LHTL or CON and analyzed for maximal Na+,K+ATPase activity (K+-stimulated 3-O-methylfluorescein phosphatase, 3-O-MFPase); and Na+,K+ATPase content ([3H]-ouabain binding sites) . 3-O-MFPase activity was decreased by -2.9±2.6% in LHTL (P<0.05) and was depressed immediately after exercise (P<0.05), similarly in CON and LHTL (-13.0±3.2; and -11.8±1.5%, respectively). Plasma [K+] during exercise was unchanged by LHTL; [3H]-ouabain binding was unchanged with LHTL or exercise. VO2peak was reduced in LHTL (P<0.05) but not in CON, whilst exercise work was unchanged in either group. Thus LHTL had a minor effect on, and incremental exercise reduced Na+,K+ATPase activity. However, the small LHTL-induced depression of 3-O-MFPase activity was insufficient to adversely affect either K+ regulation, or total work performed.
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